In order to fully exploit knowledge garnered from sequencing the human genome, there is a dire need to deliver biologically active drugs and biopharmaceuticals into the CNS for stroke therapies and the treatment of neurodegenerative disease. The goal of this exploratory R21 feasibility research proposal is to identify peptides capable of targeting the choroid plexus (CP) so that they can be evaluated for their capacity to deliver drugs to the CP or across the CP into cerebrospinal fluid (CSF). The anatomical and therapeutic rationale for the proposed research originates with the observation that the CP is a structurally unique interface between blood and CSF that acts as a heretofore unrecognized focal gateway that can deliver naturally occurring agents like ascorbic acid into the brain, and specifically into CSF. Accordingly, in addition to drug targeting the CNS, CP-targeting would also open the possibility of creating new CP-based neurotherapeutics that either (1) modify CP drug transport functions directly, (2) alter its capacity to secrete CSF or (3) modulate the composition and concentration of factors (e.g. growth factors) that it places into CSF. Rather then apply rational design to create drug delivery agents for CP and CSF therapeutics however, we propose to exploit the power of combinatorial biology and genetic selection to mine libraries of peptides for those capable of targeting CP. Specifically, we propose to identify (1) peptides that target CP endothelial and stromal cells (2) peptides that target CP epithelial cells and (3) peptides that can translocate across the CP and into CSF. At the conclusion of this project, we will have identified 3 classes of peptides capable of specifically targeting the blood (basolateral) and CSF (apical) interfaces of the CP for CP and CSF-targeted for drug delivery to the brain during neurodegeneratrive disease.